1. What Effect Do Ultraviolet Rays Have On Yeast Colony Growth?
By Katie Schneider
Grade 10
Academy of Notre Dame de Namur
Take out school.

2. Research
UV-A light, specifically, is what mainly causes tanning, skin aging, and cataracts, UV-B causes sunburn, skin aging and skin cancer, and UV-C is the strongest, and therefore most effective at killing microorganisms. Sunburn is a short-term sign of UV damage, but skin aging and skin cancer are long-term effects of UV damage.
I would make this multiple bullets.

3. Research
UVA radiation specifically causes 2 types of DNA damage: cyclobutane pyrimidine dimers and 6-4 photoproducts, both of which cause bends in DNA structure, therefore hindering replication and transcription. These 2 types of damage are repaired by nucleotide excision repair, in which the damage is detected, the section of DNA that includes the damage is removed, and it is filled in with new DNA by DNA polymerase.
Again – single words and multiple bullets.

4. Research
In this experiment, the Saccharomyces cerivisiae is genetically engineered to be DNA-repair-deficient. This means that the enzymes that normally would repair DNA damage are knocked out so that the yeast is especially sensitive to UV light. This helps to show what effect that gene has in yeast’s lives, and how fatal UV light would be if the DNA damage was not repaired.
Too many words – single words – you are going to SAY the rest.

5. Hypothesis
If yeast colonies are exposed to UV light for varied amounts of time, a short amount of UV exposure will aid in yeast production, but longer exposure will kill the yeast cells because of the damaging effects of UV light.

6. Materials UV-sensitive yeast strain Sterile dilution tubes
Sterile toothpicks
Dextrose (YED)
Petri dishes
Sterile distilled water
Pipettes
Glass spreading beads
Where was yeast purchased? I would put materials on just one page – make two columns.

7. Materials Disposable gloves Microwave oven Permanent marker
Aluminum foil
Stopwatch
Cardboard box
3 UV flashlights
Transparent sticker with 34 sections

8. Procedure
The agar plates were poured by heating sterile YED agar in a microwave then pouring the agar onto 25 petri dishes
The master plate was then streaked with yeast
To determine the optimal serial dilution needed for the experiment, 1:1,000 and 1:10,000 dilutions of a yeast suspension made from the growth on the master plate were tested
They showed no growth, so they were tested again, but without UV exposure
They again showed no growth, so 1:10 and 1:100 dilutions were tested
The 1:10 dilution provided growth that was too dense, so 1:100 dilution was used for actual experimentation
Plastic test tubes and sterile bulb pipettes were then used to make the 1:100 serial dilution of the yeast suspension

9. Procedure
2.5 mL of this suspension was pipetted into each petri dish, which was labeled either exposed or control for 1, 3, 5, or 7 minutes, with 3 trials for each
5 glass beads were placed in each petri dish, which were swirled across the plate to spread the yeast suspension
Three holes were made across the middle of a cardboard box, and UV flashlights emitting light in the 385 nm range were places in the openings
Three petri dishes at a time were then exposed to the light for their indicated times
Controls were covered in aluminum foil before being exposed to the UV light
The exposed samples were then covered in aluminum foil, and stored in an incubator for 2 days at 30°C

10. Procedure
To collect the data, a transparent grid containing 34 sections was placed over the petri dish
The number of sections containing yeast growth out of 34 was then recorded
There were 3 trials for each amount of time for control and exposed
Independent variable-the amount of time the yeast was exposed to UV light
Dependent variable-the amount of yeast growth
Control-the yeast not exposed to UV light
Constants-amount of yeast in each petri dish, sixe of the petri dishes,
Make your variables a separate slide.

11. Number of Sections Showing Yeast Growth out of 34
Data
Number of Sections Showing Yeast Growth out of 34
Trial #
Control 1 min
Exposed 1 min
Control 3 min
Exposed 3 min
Control 5 min
Exposed 5 min
Control 7 min
Exposed 7 min 1 34 18 30 2 32 26 33 3
Average 22 29 21 31 23

12. Data

13. Conclusion
Hypothesis-“a short amount of time will aid in yeast production, but a longer amount of time will kill the yeast cells because of the damaging effects of UV light.”
The results support the hypothesis, however, because of the high standard deviation, the results were proven to be unreliable.
This experiment has relevance to the world today because UV light is a major cause of skin cancer, and extended exposure can be extremely detrimental to skin health.
Other experiments regarding UV light could be conducted testing the strength of UV at different times of day, during different seasons, or for longer periods of time.
You need a slide with sources of error.
Watch the wording in bullet 2 (were proven to be unreliable – I would say that they may be unreliable – more trials are suggested).

14. References
Cells and DNA. (2011, October 17). Retrieved from
Clancy, S. (2008). DNA Damage & Repair: Mechanisms for Maintaining DNA
Integrity. Retrieved from Nature Education database.
Deoxyribonucleic Acid (DNA). (2011, March 23). Retrieved from
DNA damage from deamination and depurination [illustration]. (n.d.). Retrieved from Science Online database.
Genetic Engineering. (2011, May 23). Retrieved from
Goodman, B., MA. (2011, October 6). UVA Radiation May Cause DNA Damage in Skin. Retrieved from
Highland, J. (n.d.). The Effects of UV Light on Yeast. Retrieved from
Hockberger, P. E. (2002). History of Ultraviolet Photobiology. Retrieved from Department of Physiology, Feinberg School of Medicine, Northwestern University website:
Kirkland, K., PhD. (2007). Infrared and Ultraviolet. In Light and Optics (pp ). New York: Facts On File, Inc.
Liu, S., & Usinger, L. (n.d.). All About Agar. Retrieved from
MacNeal, R. J., MD. (2007, August). Overview of Sunlight and Skin Damage. Retrieved from Merck website:

15. References
Maczulak, A. (n.d.). Saccharomyces. In Encyclopedia of Microbiology. Retrieved from
Tanner, F. W., & Ryder, E. (1923, May). Action of Ultraviolet Light on Yeast-Like Fungi. Botanical Gazette, 75(3), 309. Retrieved from
Twyman, R. (2002, August 28). What are ‘model organisms’? Retrieved from
Ultraviolet radiation and human health. (2009, December). Retrieved from World Health Organization database.
Ultraviolet treatment for water suggested. (2010). Biofouling. Retrieved from
Ultraviolet (UV) Radiation. (2010, August 17). Retrieved from
Whyte, D. B. (2009, December 4). Exploring DNA Damage: What Effect Do Ultraviolet Rays Have on Yeast Colony Growth? .
Wyman, B., & Stevenson, H. L. (n.d.). Ultraviolet radiation–A range (UV-A). In The Facts On File Dictionary of Environmental Science, Third Edition. Retrieved from
Wyman, B., & Stevenson, H. L. (n.d.). Ultraviolet radiation–B range (UV-B). In The Facts On File Dictionary of Environmental Science, Third Edition. Retrieved from
Wyman, B., & Stevenson, H. L. (n.d.). Ultraviolet radiation–C range (UV-C). In The Facts On File Dictionary of Environmental Science, Third Edition. Retrieved from